1. Field of the Invention
The invention relates generally to air conditioning systems and, in particular aspects, to devices and methods for controlling humidity during air conditioning cycles.
2. Description of the Related Art
Indoor air quality has become a significant concern, particularly for homes, but also for office buildings where workers spend much of their day. There are some concerns that poorly ventilated indoor spaces permit contaminants in the interior air to become concentrated as the air is recirculated. One part of this perceived problem is that of toxic mold.
Air conditioning serves two basic purposes. The first is the removal of heat from the air within the home or other structure. The second function is the removal of moisture, or humidity, in the air. In order to effectively remove humidity, the air conditioner must run long enough for the evaporator coil to become cold enough to remove moisture from the conditioned air. The inventor has recognized that the typical run time must be between 7–10 minutes before this moisture removal process begins.
The problems related to poor indoor air quality may be increased in newer homes, which have sought to become more energy efficient. Newer homes typically feature tighter overall construction, meaning that they permit less fresh air to permeate the structure of the home. Windows and doors, for example, are provided with tighter seals. In addition, many newer homes are provided with “low emittance” windows that provide a fluid barrier between two panes of glass. Less heat is transmitted through these windows. The tightness of the structure and the windows effectively reduces the amount of air conditioning or heating required to maintain a desired temperature within the home. However, these measures also lead to more “stale air” in the home and may exacerbate indoor air quality problems. Because the home (or other structure) permits less heat and outdoor air to enter the home naturally, a shorter air conditioning run time is required to maintain the desired temperature within the home. As a result, moisture is not effectively removed from the air.
Standards have been developed recently that require the introduction of fresh outside air in conjunction with the typical air conditioning cycle of a home. ASHRAE Standard 62-89, “Ventilation for Acceptable Indoor Air Quality,” which is incorporated into many building codes, recommends that the relative humidity of homes be maintained between 30 and 60 percent in order to minimize the growth of allergenic and pathogenic organisms. As a result, the air conditioning system for many new homes incorporates a motorized “outside air” damper that selectively introduces outside air into the system. An air cycle timer operates the motorized damper and indoor blower so that outside air is introduced according to a predetermined time schedule. Often, the outside air damper will introduce extremely humid air into the home, raising the humidity level above the 60% level recommended by the current ASHRAE standard.
The inventor has recognized that, during the initial portion of the cooling cycle, very warm and humid air is also introduced into the home even via closed air conditioning systems. The plenum, duct work and, often, the blower, is typically located in the attic of a home and, thus, are subjected to hot summertime temperatures. It is not uncommon for the air introduced into the home in the initial stages of the initial portion of the cooling cycle to be around 130 degrees F. This initial injection of warm and humid air significantly increases the temperature and humidity in the air within the home during the start of an air conditioning cycle. If the air conditioning cycle is short, it does not effectively remove the humidity.
Some techniques have been developed for removing moisture from indoor air. Unfortunately, these techniques are expensive and largely ineffective. Newer furnaces/air handlers, for instance, have been developed that are provided with special motors that can adjust motor speed by varying voltage to the motor. The speed control for these units is provided by way of predetermined logic via printed circuit boards within the control system of the unit. These “variable speed furnaces” require a specialized D/C motor, are quite expensive as are replacement motors for them. The variable speed furnaces have additional features that can create problems if not accommodated in the design of the air conditioning system. Additionally, it is pointed out that these variable speed units are limited in reducing the blower speed sufficiently to be able to effectively remove moisture. Most such units limit the lower end of blower speed to approximately 80% of the blower's full speed, which does not accelerate dehumidification in the cycle significantly. Additionally, D/C motors have difficulty withstanding A/C voltage drops and surges. This leads to a higher failure rate than for furnaces that incorporate A/C motors.
U.S. Pat. No. 6,431,268 issued to Rudd describes a system for controlling operation of an air conditioning system wherein a controller (“air cycler timer”) operates an outside air damper. With Rudd's device, the damper is opened and the air distribution fan is energized on a timed on and off cycle. If the air distribution fan is already in operation due to a cooling demand from the thermostat, Rudd's air cycler will energize only the damper for a preset timed period. Rudd's system does not positively control the outside air damper with respect to humidity level and does not independently, or as a byproduct of operation, have any effect on dehumidification.
U.S. Pat. No. 6,223,543 issued to Sandelman describes an air conditioning system that incorporates a fan speed controller that is connected to the system fan to variably control the speed of the fan. Sandelman's system measures dry bulb temperature and moisture levels and then adjusts the fan speed based upon those measurements. Sandelman's system does not reliably provide for reduced speed operation of the blower during initial portions of the blower cycle. Also, the system is relatively complex since it relies upon temperature and moisture sensing to operate and utilizes a programmed controller. In practice, Sandelman's system also requires a specialized variable speed motor so that the fan speed can be controlled. This type of motor is expensive. This complexity also makes the system difficult to troubleshoot and somewhat costly.
U.S. Patent Application Publication No. U.S. 2002/0124992 A1 by Rainer et al. describes an integrated ventilation cooling system that incorporates an electronically commutated, variable speed motor, or “ECM,” for control of the blower fan. As Rainer admits, ECMs do not provide a significant speed reduction (only around 20% variance in airflow). Additionally, ECMs are specialized equipment and costly. Operation of the ECM in Rainer's arrangement is tied directly to the difference between the actual indoor temperature and the desired temperature. When the difference is great, the ECM causes the blower to operate at a greater speed. When the difference is less, the ECM causes the blower to operate at a lower speed. Thus, fan speed is based entirely upon temperature and not humidity levels.
There is a need to provide improved methods and devices for removal of moisture from indoor air. The present invention addresses the problems of the prior art.